1. Field of the Invention
The present invention relates to a data input/output technique, and particularly to a technique for input/output of encrypted data, which is to be kept secret, between a storage device and a host device.
2. Description of the Related Art
As a contents data distribution system with improved security of license data, a contents data distribution system disclosed in Japanese Patent Application Laid-open No. 2004-133654 is known, for example. With such a system, the devices handling the license data in the non-encrypted form are classified into three kinds of devices, i.e., a server, a memory card (storage device), and a decoder (user device). Transmission/reception of the license data is performed between the devices (between the server and the storage device, or between the storage device and the user device) through an encrypted communication path established therebetween. Note that each of the server, the storage device, and the user device, includes a TRM (Tamper Resistant Module) for handling the license data in the non-encrypted form.
With establishment of the encrypted communication path, first, a device receiving license data (which will be referred to as “license receiver”) transmits a certificate including a public key to a device providing the license data (which will be referred to as “license provider”). Then, the license provider verifies the certificate of the license receiver. As a result of the verification, only in a case that determination has been made that the certificate is valid, key sharing is performed between the two devices using the public key of the license receiver included in the certificate. Then, the license data is encrypted using two keys transmitted from the license receiver. The encrypted license data is transmitted from the license provider to the license receiver. One of the aforementioned two key is a temporary symmetric key. The other is a public key which is individually stored by the license receiver.
The TRM is a circuit module which physically protects the security thereof. The TRM has a configuration which protects itself from access from external circuits, except through the encrypted communication path.
Note that in a case of acquisition of the license data, the memory card, which is mounted to a terminal having a function of communication with the server, receives the license data from the server through the terminal. On the other hand, in a case of using contents, the memory card, which is mounted to the terminal including a built-in decoder, transmits the license data to the decoder through the terminal.
As described above, such a contents distribution service provides encryption of the contents data and security of the license data, thereby ensuring copyright protection with regard to the contents. Such ensuring of the contents copyright protection protects the right of the copyright holder of the contents, thereby providing contents with high security. This helps to increase the lineup of contents available as distribution services, thereby meeting the needs of the user over a wider range.
Video contents having a specification of the high-definition TV are being widespread. Here, video contents having a specification of high-definition TVs will be referred to as “HD contents”. On the other hand, video contents having a specification of conventional TVs will be referred to as “SD contents”.
HD contents have a larger data amount per unit time than that of the SD contents. For example, with the MPEG2 method employed in digital broadcasting, the HD contents have approximately three times the date amount per unit time of that of the SD contents. Such a system handling a large data amount requires higher-speed access of the storage device storing the HD contents.
Now, let us consider an arrangement in which the copyright protection function of the conventional systems is applied to such HD contents. With the conventional systems, transmission/reception of the license data is performed using the public key encryption system. The public key encryption system requires longer time than with the symmetric key encryptosystem. That is to say, with the conventional systems, transmission/reception of the license data requires access time corresponding to computation time for the public key encryptosystem.
In a case that the license data is recorded in increments of programs or the like, and the programs are reproduced in increments of programs, the system accesses the license data with a low frequency. Accordingly, in this case, the access time is negligible. On the other hand, in a case of providing special reproduction (skip reproduction, program reproduction which is reproduction of parts of multiple programs following a sequence programmed by the user, and so forth), the system accesses the license data with a higher frequency. Accordingly, such special reproduction requires higher-speed access of the license data.